Keep the radios. Add everywhere they cannot reach

A DMR or analogue system covers the site it was built for and stops at the fence. push.tt covers wherever there is cellular. A bridge joins the two, so the crew on handhelds and the driver two counties away are on the same conversation — without replacing equipment that works.

Describe your system What it costs you

In development. Not built. This is the design and, more importantly, the list of things that make it harder than it sounds — including one that costs you something real and cannot be engineered away.

What a bridge actually is

Two ways in, and which one applies depends on what you already own rather than on what we would prefer to build.

A donor radio. A spare handset or mobile on your channel, wired to a gateway that keys it when somebody talks on push.tt and relays its audio back the other way. Works with anything — analogue, DMR, P25, TETRA — because it speaks the only universal interface a radio has: audio and PTT
A network interface. DMR Tier III, P25 ISSI/CSSI and most modern trunked systems expose a documented gateway. Cleaner, keeps talkgroup identity intact, and needs your vendor's cooperation and usually their licence
Mapping is per talkgroup, not per system. One radio talkgroup to one push.tt channel, so an operation can bridge dispatch without bridging everything

What a bridge costs you

This is the section that would be missing from most vendors' version of this page, and it is the one that should decide whether you do it.

Bridged traffic is not end-to-end encrypted, and cannot be. A DMR radio holds no push.tt key and never will. For audio to reach it, something has to decrypt — so at the gateway, that conversation exists in plaintext. There is no clever construction that avoids this; it is what bridging to a device that cannot do the maths means
What we would do about it: the gateway runs on your premises rather than ours, so the plaintext is inside your building and not on our servers; bridged channels are labelled as such in the app, the way server-side transcription already is; and unbridged channels are completely unaffected
Vocoders are licensed. DMR and P25 use AMBE codecs that are proprietary. Transcoding needs licensed hardware or software, and that is a per-channel cost somebody has to pay — a donor radio sidesteps it entirely by staying in the analogue domain
Latency stacks. Cellular, plus the gateway, plus the radio system's own delay. Fine for dispatch; noticeable if two people are used to instant hand-offs
Floor control gets a second opinion. Both sides can key up at once and neither knows about the other, so somebody has to lose. That rule has to be chosen deliberately rather than discovered during an incident

What you get for it

Assuming the above is acceptable, the reason to do this at all:

Coverage stops being a map. Anyone on a phone joins the radio net from anywhere with a signal — no repeater, no licence, no coverage survey
The people who need radios keep them. Intrinsically safe, licensed, works in the tunnel where cellular does not — a bridge adds reach without arguing with any of that
Dispatch sees one picture. The command console shows both populations in one place rather than a radio on the desk beside a screen
Retention and audit cover the bridged channel too, which for most radio systems is the first time that traffic has ever been recorded searchably

What we would need to know

The questions that decide whether this is weeks or quarters:

Which system, and whether it is analogue, DMR (Tier II or III), P25 or TETRA
Whether your radio vendor will give you network access, or whether a donor radio is the realistic path
How many talkgroups actually need bridging — it is usually one or two, not all of them
Whether anyone would object to that traffic existing in plaintext at the gateway, because that is the question, and it is better asked now

Describe the system

Make, model, and whether you have network access or only a spare radio. That is enough to say which approach applies and what it costs. If you are also looking at rugged cellular handsets for the crews who do not need a licensed radio, see PoC radios.

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